Crystal mounting with temperature compensation



y 9, 1939- H. E. HOLLMANN 2,157,665

CRYSTAL MOUNTING WITH TEMPERATURE COMPENSATION Filed Oct. 17, 1936 INVENTOR HANS E. HOLLMANN 7 m-v-OL ATTORNEY Patented May 9, 1939 UNITED STATES PATENT OFFICE CRYSTAL MOUNTING WITH TEMPERATURE COMPENSATION poration of Germany Application October 17, 1936, Serial No. 106,106 In Germany October 16, 1935 13 Claims.

This invention relates to a novel type of piezoelectric crystal mounting having temperature compensation.

In the stabilization of the frequency of electric oscillations by means of piezo crystals which are inserted in any transmitting circuit arrangement as frequency-controlling oscillation devices, there occurs, as is known, the disadvantage that the controlling crystal absorbs considerable power if the transmitter is to deliver an eflicient highfrequency output. The result thereof is a noticeable heating up of the control crystal, also a more or less large frequency distortion occurs which assumes a stable state only some time after the starting up when a temperature balance has been established. In case of irregular keying of transmitter or in telephonic modulation, a stable state of balance cannot be obtained. This is particularly true in ultra-short wave quartz or turmalin resonators, where constancy of frequency is of prime importance, in such resonators relatively strong heating occurs due primarily to the small mass of the crystal and the frequency distortion. These unfavorable conditions are so large that the success of the stabilizing measure is put in complete jeopardy.

The prior art has disclosed several methods for the purpose of eliminating these disturbing frequency effects aiming in principle at keeping the temperature of the controlling crystal as constant as possible by means of thermostats. However such thermostats have the basic disadvantage that their inertia increase as their sensitiveness decreases, in other words, the smaller the energy changed to heat in the crystal, Which is exactly the case in the small crystals for ultra-short waves. Aside from that, the great expense for the apparatus is unwarranted, exceeding in some cases even the cost for the transmitter itself.

Now, it is known that it is possible to vary by purely electric means the frequency of a piezocrystal within certain limits by connecting a variable capacity in series with the crystal. In place of a special series condenser, the distance between a crystal surface and the auxiliary electrode located over it can also be varied directly which likewise results in a variation of the series capacity. If the size of this series capacity is brought in direct relationship to the temperature of the crystal, for instance by automatically varying the distance between crystal and electrode by means of a bimetallic strip, the automatic compensation of the frequency distortion, due to heating of the crystal, can easily be accomplished by a corresponding variation of the series capacity.

This thermo-mechanical compensation method has still a disadvantage common to all thermostats for the reason that sufiicient heat quantities must be available to render effective the compensation. For the removal of this difficulty the present invention proposed to combine the control crystal by means of a common casing used in its mounting with a suitable series capacity, whose dielectric has according to the temperature coefficient a positive or negative temperature coefficient, to a thermic unit so that with the heating of the crystal a quick heat exchange takes place with the series condenser. In accordance with the invention, the temperature coefficient and the size of the series condenser are balanced in the manner that the purely thermic capacity variation just compensates the frequency distortion of the control crystal.

This invention will best be understood by referring to the accompanying drawing, in which:

Fig. l is a sectional view of a crystal holder of this invention;

Fig. 2 is a sectional view of a crystal holder of this invention in which the crystal and the condenser dielectric are combined.

Fig. 1 illustrates a practical embodiment of the invention by way of example, showing in section a crystal mounting or casing having an internal rim forming a support for a plurality of electrodes, which arrangement, according to the invention, makes the crystal in series with a condenser. K is the crystal disposed in the casing between the two electrodes P and P. The lower electrode on which the crystal rests is kept as thin as possible with a view to facilitate the passage of heat and represents at the same time the one coating or electrode of series condenser C which the temperature compensation. In order to render the course of the heat as uniform as possible through the entire mounting, it appears suitable to place the mounting under vacuum.

Fig. 2 finally shows a simplification of the practical application of the principle of the invention,

that is a crystal mounting, whose housing consists of a casing of ceramic material exclusively, the bottom being depressed-forming at the same time the dielectric for the compensating capacity. The crystal rests directly on the bottom of the housing, whose underside is provided with a ridge to secure and support a metallic coating P. No deviation from the principle of the invention occurs if also above the crystal there is disposed another solid dielectric forming a second compensating capacity, for instance in the manner that the mounting according to Fig. 2 in addition to the bottom portion of the casing is closed with an insulating cover, which acts otherwise exactly as the bottom portion.

These examples may suffice for the practical visualization of the idea of the invention which, of course, is subject tonumerous variations.

What is claimed is:

1. A piezo-electric crystal holder comprising a casing of dielectric material, a crystal within the holder, a condenser incorporated in the holder, a portion of said casing constituting the condenser dielectric, said dielectric material having a temperature coefficient of specific inductive capacity determined by the temperature coefiicient of frequency of the crystal, electrodes for said crystal and condenser, at least one of the electrodes being located at the top of the casing and another at the bottom thereof.

2. A piezo-electric crystal holder comprising a casing of dielectric material, a crystal within the holder, a condenser incorporated in the holder, the bottom portion of said casing constituting the condenser dielectric, said dielectric material having a temperature coeflicient of specific inductive capacity determined by the temperature coefficient of frequency of the crystal, electrodes for said crystal and condenser, at least one of the electrodes being located at the top of the casing and another at the bottom thereof.

3. A piezo-electric crystal holder comprising a casing of dielectric material, a crystal within the holder, a condenser incorporated in the holder, at least one of the end portions of said casing constituting the condenser dielectric, said dielectric material having a temperature coefiicient of specific inductive capacity determined by the temperature coefficient of frequency of the crystal, electrodes for said crystal and condenser, at least one of the electrodes being located at the top of the casing and another at the bottom thereof.

4. A piezo-electric crystal holder comprising a casing of ceramic dielectric material, a crystal within said holder, a condenser incorporated in the holder, a portion of said casing constituting the condenser dielectric, said dielectric material having a temperature coefficient of specific inductive capacity determined by the temperature coeflicient of the frequency of the crystal, electrodes for said crystal and condenser, at least one of the electrodes being located at the top of the casing and another at the bottom thereof.

5. A piezo-electric crystal holder comprising a casing having its walls and bottom portion of a solid dielectric material, a crystal within the holder, a condenser incorporated in the holder,

said bottom portion of said casing constituting the condenser dielectric, said dielectric material having a temperature coeificient of specific inductive capacity determined by the temperature coefficient of frequency of the crystal, electrodes forsaid crystal and condenser, at least one of the electrodes being located at the top of the casing and another at the bottom thereof.

6. A piezo-electric crystal holder comprising a casing having a rim portion of dielectric material, a crystal within the holder, a condenser incorporated in the holder, a portion of said casing constituting the condenser dielectric, said dielectric material having a temperature coefficient of specific inductive capacity determined by the temperature coefficient of frequency of the crystal, electrodes for said crystal and condenser, and a plurality of said electrodes supported by said rim portion, one of said electrodes being located at the top of the casing and another at the bottom thereof.

7. A piezo-electric crystal unit comprising a holder of dielectric material, a crystal in said holder, a condenser incorporated in the holder, a portion of said holder constituting the condenser dielectric, said dielectric material having a temperature coefiicient of specific inductive capacity determined by the temperature coefiicient of the frequency of the crystal, electrodes for said crystal and condenser, at least one of said electrodes being located adjacent one face of said ing walls of said casing, a solid dielectric Ofj. ceramic material for said condenser in series with said crystal and said electrodes, the material of said dielectric having a temperature coefficient of specific inductive capacity determined by the temperature coefiicient of the frequency of the;

crystal.

10. A piezo-electric crystal holder comprising a casing, a crystal within said holder, a condenser incorporated in said holder, a first and a second electrode located at the ends of said casing, a

solid dielectric, and a third electrode for said condenser in series with said crystal and said first and second electrodes, the material of said dielectric having a temperature coefiicient of specific inductive capacity determined by the tem-,-:,

perature coefficientof the frequency of the crystal.

11. A piezo-electric crystal holder comprising a casing, a crystal within said holder, a condenser incorporated in said holder, a first and a second.

electrode located at the ends of said casing, a solid dielectric for said condenser, a thin metallic coating on at least one side of said crystal forming a third electrode, said solid dielectric and said third electrode being in series with said crystal and said first and second electrodes, the material of said dielectric having a temperature coefficient of specific inductive capacity determinedby the temperature coeficient of the frequency of the crystal.

12. A piezo-electric crystal unit comprising a holder, a crystal within said holder, a condenser incorporated in said holder, electrodes for said crystal and condenser, at least one of the electrodes :being located adjacent one face of said crystal and another electrode adjacent another face of said crystal, and a solid dielectric for said condenser in series with said crystal and said electrodes, the material of said dielectric having a temperature coelficient of specific inductive capacity determined by the temperature coefiicient of the frequency of the crystal.

13. A piezo-electric crystal holder comprising a casing of dielectric material, a crystal within the holder, a condenser incorporated in the holder, said condenser having two solid dielectrics, one of which is disposed on a face of said crystal, a portion of said casing constituting the other condenser dielectric, the material of said dielectrics having a temperature coefiicient of specific inductive capacity determined by the temperature coefiicient of frequency of the crystal, electrodes for said crystal and condenser, at least one of the electrodes being located at the top of the casing and another at the bottom thereof HANS ERICH HOILMANN. 

